Acid, galvanic zinc bath

ABSTRACT

An acid, galvanic zinc bath free of organic zinc complexing or zinc-sequestering compound for the deposition of bright high luster zinc coatings.

United States Patent 11 1 Todt et a]. June 24, 1975 ACID, GALVANIC ZINC BATH [56] References Cited [75] Inventors: l-Ians-Giinther Todt; Giinter Voss, UNITED STATES PATENTS both of Berlin, Germany 3.594.291 7/1971 Todt et a]. 204/55 R Assignee: schering Berlin & Bergkamen, 3,694,330 9/I972 Korplum et a]. 204/55 R Germany FOREIGN PATENTS OR APPLICATIONS 22 Filed; Jam 29 1973 I,524,7I9 4/I968 France 204/55 R [2]] Appl' Primary ExaminerF. C. Edmundson R l d U,s A li aflon D m Attorney, Agem, or Firm-Joseph F. Padlon [63] Continuation of Ser. No. 27,164, April 9, I970,

abandoned. I 57] ABSTRACT An acid, galvanic zinc bath free of organic zinc com- [52] US. Cl. 204/55 R; 204/DIG. 2 l i or i questering compound for the deposi- [51] Int. Cl C23!) 5/12 {ion of bright high luster Zinc coatings. [58] Field of Search 204/55 R, DIG. 2

4 Claims, No Drawings ACID, GALVANIC ZINC BATH This is a continuation of application Ser. No. 37.l64 filed Apr. 9 70 now abandoned.

The invention relates to an acid. electrolyte free of organic zinc-complexing or zinc-sequestering compounds for the deposit of bright to high-luster zinc coats.

In practice. alkaline. cyanide containing zinc baths are most widely used containing the zinc as a mixture of the hydroxoand cyanide complexes. These baths have various disadvantages. such as: the cyanide content is a constant danger for the people working at the bath; the baths being subject to constant aging by decomposition of the cyanide and formation of carbon atoms; the waste water must be subjected to a costly treatment to destroy the cyanide ions and to precipitate the zinc as hydroxide therefrom.

It has been tried to replace the toxic cyanide by more harmless complex-formers; for example. by ethylene diamine tetraacetic acid or similar sequestering or complex-forming compounds. However. this does not bring any substantial advantages in the decontamination of the waste water. because the complexes are mostly very stable and the zinc cannot be precipitated by simple neutralization as a hydroxide. The same expensive waste water treatment is thus required as with cyanidecontaining zinc baths. ln addition. it was found that these electrolytes are highly sensitive to contaminations by foreign metals. such as. iron. copper or nickel. Even minute quantities of these metals lead to a considerable deterioration of the luster of the deposited coats and to defects in the subsequent chromatization.

The waste water treatment in acid zinc baths free of organic zinc-complexing compounds and where the zinc is present in the form of free Mn ions presents no problems. Here a simple neutralization is sufficient to precipitate the zinc as a hydroxide. Electrolytes of this type. which are prepared with zinc sulfate or zinc chloride. Zinc fluoroborate or zinc sulfamate and which contain normally also conducting salts and. if necessary. boric acid. are known. They are used. for example. for galvanizing wires or strips by drawing. The zinc deposit here is not bright. but finely crystalline and dull. Besides. the throwing power of these electrolytes is very poor. It has also been suggested to use acid zinc baths which permit the deposit of bright coats and which contain organic substances in small quantities as luster-formers.

Thus. it is known from DAS N0. 1.253.986 to add to the zinc baths primary amines with at least four carbon atoms in the molecule and water-soluble condensation products of naphthalene sulfonic acid with formaldehyde. The amines. which are used in quantities of 0.2 to g/liter and more. are typical complex-formers. However. they present difficulties in the waste water treatment. Particularly when the waste water contains at the same time copperor nickel-ions from other galvanic baths. the heavy metals can no longer be precipitated by simple neutralization.

The imide azolinium compounds described in DAS No. 1.263.445 are likewise complexformers with the above described disadvantages. They are added to the zinc baths in relatively large quantities of l to 100 g/liter. but by themselves they yield only poor luster effects. They must therefore be used together with known luster-formers. like gelatin and pipersonal. But

their disadvantages are also manifest themselves. each being. for example. instability in the electrolyte. brittleness and poor adhesion of the zinc coats to the subsurface or substrate.

Another combination of luster-formers indicated in DAS No. 1.266.097 consists of meat-protein hydrolyzate and aldehydes. the latter in the form of their bisulfite-addition compounds. Zinc baths with these additives. however. tend to deposit pitted. relief-like coats and the luster region is extremely narrow. that is. at low current densities. the zinc coats are dull.

Finally. Dutch Pat. application No. 67.069l9 describes acid zinc-baths which contain as luster-formers an aromatic carbonyl compound. a non-homogeneous surface-active polyoxyethylene compound. ammonium chloride and/or another compound forming soluble complex-formers with zinc salts in the pH-region between 2.5 and 5.5. These electrolytes cannot be operated by injection of air, since intensive foaming appears with the necessary content of surface-active polyoxyethylene compounds of 0.5 to 20 g/liter. Consequently. it is not possible to use such high current densities and to achieve such high depositing rates as with air injection and the resulting intensive electrolyte movement.

High depositing rates are a very important factor. however. in practice for the use of an electrolyte. because of the better balancing of the bath and of the galvanizing plant resp. Air injection also increases the luster of the zinc coats and the smoothing of roughnesses of the base material; thus achieving a definite improvement in quality. Many aromatic carbonyl compounds. particularly aldehydes and carbonylic acids. yield in addition in combination with surfaceactive polyoxyethylene compounds relief-like dark zinc coats. or coats which are only bright in a very narrow current density range.

It has already been suggested to use zinc baths which contain compounds of the general formula and N-polyvinyl pyrrolidon-(2). But coats deposited from these baths tend to form microcracks at coat thicknesses above about 20 mpt. due to their brittleness.

The object ofthe present invention application therefore is to eliminate the disadvantages of the above mentioned zinc baths and to permit the deposit of bright to high-luster coats with good throwing power. which are ductile even at great coat thicknesses. Another object is to have electrolytes which are free of organic zinccomplexing compounds in order to permit waste water decontamination by simple neutralization.

The solution of this problem is achieved according to the invention by the use of acid galvanic zinc baths which contain no complex-formers and which are characterized in that they contain a. at least one compound of the general formula wherein n denotes an integral number from 5 to 500. preferably from 20 to 200; and (b) one or more compounds of the general formula wherein R and R are identical or different and an aryl radical, a cumarinyl radical or a fiveor sixmember heterocyclic radical with one or more N- and- /or 5- and/or 0-,atoms. the radicals being linked, if necessary. over a saturated or unsaturated hydrocarbon chain with preferably up to four carbon atoms with the CO- group, or a phenylcarbonyl alkyl radical. or where R, has the indicated meaning and R denotes a saturated or unsaturated aliphatic hydrocarbon radical with preferably l to 4 carbon atoms. an alkoxycarbonylalkyl radical or an alkyl cyanide radical.

Particularly suitable are compounds where R, and R in the general formula are identical or different and which represent the radicals phenyl. naphthyl, connected. if necessary. over a vinylene chain with the CO- group, or the radical bra wherein Y denotes an alkyland/or alkoxy group and n is an integral number from I to 3, or phenylcarbonylmethyl, or wherein R has the above indicated meaning and R denotes a saturated aliphatic hydrocarbon radical with preferably l to 4 carbon atoms. low alkoxycarbonylmethyl or methyl cyanide.

The substituents X and Y can be monoor trisubstitute the phenyl or pyridine nucleus in identical or different mannerv As examples of substituents. we mention: for X halogen. such as fluorine, chlorine or bromine and others. a low alkyl, like methyl. ethyl and others. and alkyl halide, like methyl trifluoride and others, the hydroxyl group. low alkoxy. like methoxy. ethoxy and others, and the CN- group; for Y, a low alkyl. like methyl. ethyl and others. and low alkoxy, like methoxy. ethoxy and others.

As saturated or unsaturated aliphatic hydrocarbon chains for linking the aryl radicals or heterocyclic radicals with the COgroup if desired. we mention: methylene, ethylene, propylene. vinylene, etc.

As alkoxycarbonylalkyl radicals. we mention by way of example: the methoxycarbonylmethyb, ethoxycarbonylmethyland propoxycarbonylmethyl radical or the corresponding ethyl-, propylor vinyl radicals. etc. and as alkyl cyanide radicals, for example, methyl cyanide and ethyl cyanide, etc.

As saturated or unsaturated aliphatic hydrocarbon radicals, we mention finally by way of example: methyl, ethyl. propyl. isopropyl. butyl, tert. butyl, ethinyl, ethenyl. propenyl, butinyl, etc.

The individual components seem to influence each other in the bath, since the improvement found goes surprisingly beyond the expected additive effect of the individual components.

The individual components show therefore the desired effect only when used together in the path of the present invention. By themselves. neither the ketones, under (b) above, nor the polyethylene glycols. under (a) above. yield satisfactory results.

The additives to be used according to the invention are known in themselves and can be produced in the usual manner. known in the art.

The degree of polymerization of the polyethylene glycols used can vary within wide limits and ranges. for example. from about 5 to 500. Preferred are products with a mean molecular weight of about 1000 to l0.000, that is, with a degree of polymerization of 20 to 200.

The following table contains. by way of example. a list of known compounds which can used according to the invention in acid zinc baths together with polyethylene-glycols.

Name of Compound Formula Acetophenone Ethinylphcnylketone Propiophenone Benzalacetone 2 Hydroxybemalacetonc 3-Mcthoxyhcnzalacetone llflC chloride (ZnChl ammonium chloride (NH .Cl)

50 200 g/liter 50 30o g/liter Instead of zinc chloride. there can be used. at least partly. other zinc salts such as zinc sulfate, zinc acetate. zinc fluoroborate or zinc sulfamate. Ammonium chloride can be replaced partly or completely by ammonium sulfate or other conducting salts. such as sodium chloride, sodium sulfate or similar compounds. Finally. the electrolyte can contain boric acid or aliphatic and- /or aromatic carboxylic acids or salts thereof. such as acetic acid. benzoic acid. salicylic acid. etc.

As additional additives. there can be used other conventional luster-formers. such as thio-compounds. high-molecular compounds and/or aromatic aldehydes. as well as non-foaming wetting agents, particularly short-chained alkyl sulfates.

The working conditions are as follows:

pH-value 3.0-6.0. preferably 4.5-5.5 temperature l45C. preferably 30C current density (cathodic): 0. ll0.0 A/qdm.

Electrolyte movement is effected by injection of air or by moving the cathode rods. If the luster and the depositing rate do not have to meet high standards. the electrolyte movement can be eliminated.

The luster-formers to be used according to the invention are extremely stable in the zinc electrolyte; their effectiveness does not diminish even after a very long time. They are suitable both for luster galvanization of rack goods and of mass articles in drumor bell-type apparatus. In the galvanization of rack goods. a particularly bright, haze-free luster is achieved if air is injected into the bath, since the electrolyte exchange at the EXAMPLE 1 100.0 g/litcr l50.0 g/liter zinc chloride (ZnClammonium chloride (NH,Cl)

polyethylene glycol (mean mo]. 20 g/litcr weight 4000) 3acetyl pyridine 4.0 g/liter pH-value 5.0

temperature 2 3C mean cathodic current density 60 Mqdm injection of air EXAMPLE 2 zinc chloride (ZnClfl l25.(| g/liter ammonium chloride 200.0 g/liter polyethylene glycol (mean mol. 4.0 g/liter eight 6000] thienylidene acetone 0.4 g/liter 4-methoxyhcnmic acid (potassium salt) 5.0 g/liter pHvalue 5.0 temperature 25C mean cathodic current density 4.0 Mqdm injection of air EXAMPLE 3 zinc chloride (ZnCL) I500 g/liter ammonium chloride 175.0 g/litcr polyethylene glycol (mean mol. 2.0 g/liter eight 4-000) B-acetylcumarine 0.2 g/liter salicyelic acid (potassium salt) 40 g/litcr pH-value 4.8 temperature 20C mean cathodic current density 5.0 A/qdm injection of air EXAMPLE 4 zinc chloride (ZnCl I000 g/liter ammonium chloride 100.0 g/liter boric acid 20.0 g/liter polyethylene glycol (mean mol. 2.5 g/liter weight 4000) henzalacetone 0.2 g/liter benzoic acid (potassium salt) 4.0 g/liter sodium etliylhexylsulfate 8.0 g/liter pH-value 4.8 temperature 30C mean cathodic current density 4.5 Mqdm injection of air EXAMPLE 5 zinc sulfate (ZnSOy7 H 0) 2500 g/liter ammonium chloride 120.0 g/liter polyethylene glycol (mean mol. 1.0 g/liter eight [0.000) 4hydroxybenzalaeetone (Ll g/liter Z-ethoxybenzuldehyde 0.l g/liter salicylic acid (potassium salt) 25 g/liter sodium ethylhexyl sulfate 40 g/liter pH-value 4.5 temperature 22C mean cathodic current density 4.0 )oqdm EXAMPLE 6 line sulfate (ZnSO, 7 H 0) [000 g/liter ammonium chloride I000 g/liter polyethylene glycol (mean mol. 2.0 g/liter eight L500) ethinylphenyl ketone 0.05 g/liter piperonylidene benzalacetone 0.05 g/liter benzoic acid (potassium salt) l.0 g/litcr sodium-n-octyl sulfate 2.5 g/liter pH-value 4.5 temperature 30C mean cathodic current density 3.5 A/qdm movement of objects What is claimed is:

1. An acid. galvanic zinc bath for the deposition of bright to high luster zinc coats consisting essentially of an aqueous solution of pH from about 3.0 to 6.0 containing a zinc salt selected from the group consisting of zinc chloride, zinc sulfate. zinc acetate, zinc fluoborate and Zinc sulfamate in a concentration from about 50 to 200 grams per liter. other conducting salts selected from the group consisting of ammonium chloride. ammonium sulfate. sodium chloride. and sodium sulfate in a concentration from about 50 to 300 grams per liter, and luster forming compounds selected from the group consisting of (a) polyethylene glycol of mean molecu lar weight from about 280 to 22,000. in a concentration from about 0.l to 20.0 grams per liter and (b) at least one keton e selected from the group consisting of acetophenone. ethinylphenylketone. propiophenone. benzalacetone. 2-hydroxybenzalacetone. 3-methoxybenzalacetone. benzoylacetone. benzoylacetonitrile. 3- acetylpyridine. 2.4-dihydroxy-benzophenone. benzalacetophenone. dibenzalacetone. 2-benzolypyridine. 3-bezoylpridine. 4-benzolypyridine. benzoylacetic acid ethyl ester. l-(2-furyl)-l '-buten-3-one. thienylideneacetone. di-thienylidene-acetone. 3-acetylcumarine. 4-acetylcumarine. and fi-acetylcumarine in a concentration of about 0.0l to 5.0 grams per liter.

2. A zinc bath according to claim 1, in which at least one of the components of formula (a) is contained in an amount of about 0.5 to 5.0 grams per liter. and at least one of the components of formula (b) is contained in an amount of about 0.05 to 0.3 grams per liter.

3. A zinc bath according to claim 1, which additionally contains boric acid and carboxylic acid selected from the group consisting of acetic acid, benzoic acid, salicylic acid. and 4-methoxybenzoic acid, and their salts in a concentration of about L to 5.0 grams per liter.

4. An improved method for depositing bright to high luster zinc coats on a surface comprising electrodepositing zinc from an aqueous acid bath containing a zinc salt selected from the group consisting of zinc chloride,

Zinc sulfate. zinc acetate. zinc fluoborate. and zinc sulfamate in a concentration from about 50 to 200 grams per liter. other conducting salts selected from the group consisting of ammonium chloride, ammonium sulfate. sodium chloride, and sodium sulfate in a concentration from about 50 to 300 grams per liter. and luster forming compounds selected from the group consisting of (a) polyethylene glycol of mean molecular weight from about 280 to 22.000. in a concentration from about 0.1 to 20.0 grams per liter. and (b) at least one ketone selected from the group consisting of acetophenone. ethinylphenylketone. propiophenone. benzalacetone. Z-hydroxybenzalacetone. B-methoxybenzalacetone. benzolyacetone. benzolyacetonitrile. 3-acetylpyridine. 2.4-dihydroxy-benzophenone. benzalacetophenone. dibenzalacetone. Z-benzolypyridine. 3- benzoylpyridine, 4-benzolypyridine. benzoylacetic acid ethyl ester. l-( 2-furyl)-] -buten-3-one, thienylideneacetone. di-thienylideneacetone. S-acetylcumarine. 4-acetylcumarine. and 6-acetylcumarine in a concentration of about 0.01 to 5.0 grams per liter. said bath having a pH of between about 3.0 to 6.0. being at a temperature of about l0 to 45C., and effecting electrolyte movement by injection of air. 

1. AN ACID, GALVANIC ZINC BATH FOR THE DEPOSTION OF BRIGHT TO HIGH LUSTER ZINC COATS CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF PH FROM ABOUT 3.0 TO 6.0 CONTAINING A ZINC SALT SELECTED FROM THE GROUP CONSISTING OF ZINC CHLORIDE, ZINC SULFATE, ZINC ACETATE, ZINC FLUOBORATE AND ZONC SULFAMATE IN A CONCENTRATION FROM ABOUT 50 TO 200 GRAMS PER LITER, OTHER CONDUCTING SALTS SELECTED FROM THE GROUP CONSISTING OF AMMONIUM CHLORIDE, AMMONIUM SULFATE, SODIUM CHLORIDE, AND SODIUM SULFATE IN A CONCENTRATION FROM ABOUT 50 TO 300 GRAMS PER LITER, AND LUSTER FORMING COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF (A) POLYETHYLENE GLYCOL OF MEAN MOLECULAR WEIGHT FROM ABOUT 280 TO 22,000, IN A CONCENTRATION FROM ABOUT 0.1 TO 20.0 GRAMS PER LITER AND (B) AT LEAST ONE KETONE SELECTED FROM THE GROUP CONSISTING OF ACETOPHENONE, ETHINYLPHENYLKETONE, PROPIOPHENONE, BENZALACETONE, 2-HYDROXYBENZALACETONE, 3-METHOXYBENZALACETONE, BENZOYLACETONE, BENZOYLACETONITRILE, 3-ACETYLPYRIDINE, 2,4-DIHYDROXY-BENZOPHENONE, BENZALACETOPHENONE, DIBENZALACETONE, 2-BENZOLYPYRIDINE, 3-BENZOYLPRIDE, 4-BENZOLYPYRIDINE, BENZOYLACETIC ACID ETHYL ESTER, 1-(2-FURYL)-1''-BUTEN-3-ONE, THIENYLIDENEACETONE, DI-THIENYLIDENE-ACETONE, 3-ACETYLCUMARINE, 4-ACETYLCUMARINE, AND 6-ACETYLCUMARINE IN A CONCENTRATION OF ABOUT 0.01 TO 5.0 GRAMS PER LITER.
 2. A zinc bath according to claim 1, in which at least one of the components of formula (a) is contained in an amount of about 0.5 to 5.0 grams per liter, and at least one of the components of formula (b) is contained in an amount of about 0.05 to 0.3 grams per liter.
 3. A zinc bath according to claim 1, which additionally contains boric acid and carboxylic acid selected from the group consisting of acetic acid, benzoic acid, salicylic acid, and 4-methoxybenzoic acid, and their salts in a concentration of about 1.0 to 5.0 grams per liter.
 4. An improved method for depositing bright to high luster zinc coats on a surface comprising electrodepositing zinc from an aqueous acid bath containing a zinc salt selected from the group consisting of zinc chloride, zinc sulfate, zinc acetate, zinc fluoborate, and zinc sulfamate in a concentration from about 50 to 200 grams per liter, other conducting salts selected from the group consisting of ammonium chloride, ammonium sulfate, sodium chloride, and sodium sulfate in a concentration from about 50 to 300 grams per liter, and luster forming compounds selected from the group consisting of (a) polyethylene glycol of mean molecular weight from about 280 to 22,000, in a concentration from about 0.1 to 20.0 grams per liter, and (b) at least one ketone selected from the group consisting of acetophenone, ethinylphenylketone, propiophenone, benzalacetone, 2-hydroxybenzalacetone, 3-methoxybenzalacetone, benzolyacetone, benzolyacetonitrile, 3-acetylpyridine, 2,4-dihydroxy-benzophenone, benzalacetophenone, dibenzalacetone, 2-benzolypyridine, 3-benzoylpyridine, 4-benzolypyridine, benzoylacetic acid ethyl ester, 1-(2-furyl)-1''-buten-3-one, thienylideneacetone, di-thienylideneacetone, 3-acetylcumarine, 4-acetylcumarine, and 6-acetylcumarine in a concentration of about 0.01 to 5.0 grams per liter, said bath having a pH of between about 3.0 to 6.0, being at a temperature of about 10* to 45*C., and effecting electrolyte movement by injection of air. 